Partial support is proposed for a special facility for ambulatory clinical investigation through the John Hopkins Out-Patient Clinical Research Center. Based on a 20-year previous experience of long-term out-patient investigation in a large number of disorders, the Center will provide facilities and financing for continual studies in acute and chronic medical surgical illnesses of potential significance, the nature of which precludes in-patient investigation and for which clinical research can be most effectively and economically conducted on ambulatory subjects. Patients of all age groups will be included. Special resources contributing to the understanding of such diseases will include biomathematics, epidemiologic, and compliance evaluation units. A volume of 10,000 patient-visits per year is anticipated the first year, expanding progressively to 16,000 per year in the period of five years. From among research protocols covering a wide variety of disciplines representing multiple departments of the Medical School a standing Clinical Research Center Committee, the structure of which is detailed, will select and approve specific investigations. Administrative organization, financial aspects of support for patient visits and ancillary services, personnel and staffing, and specialty units are presented in detail. Of special interest are the use of case assistants and development of computer-based methods for storing and analyzing clinical research data.